A gas turbine rotor, as is used for example in the case of types GT11 and GT13 gas turbines of the assignee of the present application, is known from publication EP-A2-1 705 339 (see FIG. 1 there). Such a gas turbine rotor is also shown in FIGS. 1 and 2 of the present application. The gas turbine rotor 10 which is shown in FIG. 1 is constructed from rotor disks which are welded together in a known manner in the direction of the axis 18 and has a compressor section 11 and a turbine section 12, between which the combustion chamber is arranged in the assembled state of the gas turbine. FIG. 3 corresponds to FIG. 5 from EP-A1-1 862 638 and shows an enlarged detail of the turbine section 11 which adjoins the combustion chamber.
In the two sections 11 and 12, a plurality of rows of rotor blades, which are not shown in FIG. 1, are fastened one behind the other in the axial direction. The rotor blades are inserted by correspondingly designed blade roots into encompassing rotor blade slots (37 in FIG. 3). A heat accumulation segment carrier 35 is formed upstream of the first rotor blade slot 37 of the turbine section 11 in the flow direction and has a multiplicity of axial heat accumulation segment slots 15 which are distributed over the circumference. Beneath the heat accumulation segment carrier 35 an encompassing cooling air slot 13 is arranged, which by means of axial cooling air holes 14 (FIG. 2) which are distributed over the circumference is exposed to admission of compressed cooling air from the compressor section of the gas turbine. The cooling air slot 13 is partially covered by bridges 36 which are spaced apart by means of gaps 38 and limit access to the cooling air slot 13 to the gaps 38.
In such gas turbine rotors, encompassing incipient cracks, or cracks 17 (FIG. 2), can occur in the slot base 16 of the cooling air slot 13 depending upon the operating mode and operating time. The incipient cracks grow further with each start-up and after reaching a specific crack depth lead to unstable crack propagation as a result of rotating bending stress and fundamentally impair the component operational safety. Therefore, incipient cracks, especially in the slot base 16 of turbine shafts, must be reliably avoided.
Corresponding strength calculations, which are conducted according to the findings with crack development, prove that the intense operationally induced heat yield during start-up of the plant, in conjunction with the high notch effect of the slot geometry according to the previous design according to FIG. 2, leads to significant alternating plastifications which cause the crack formation.
A slot geometry for newly manufactured rotors therefore takes into consideration the two criteria (heat yield as load shock and notch effect of the old slot geometry) with a wider slot for reducing the air velocity and less sharp transition radii of the slot base to the slot flanks. The previous repair methods are based on constructing the new slot geometry by means of machining out the slot, i.e. by increasing the old slot geometry. In this case, the bridges 36 of the heat accumulation segment carriers 35 are removed over the slot width, which reduces the supporting stability of the remaining bridge sections as a guide for the slot-covering cover segments, or requires the subsequent arrangement of the bridges 36 by means of welded connections and post-heat treatment of the latter.